1. Field of the Invention
This invention relates to a novel optical disc apparatus.
2. Description of the Prior Art
Optical disc apparatuses are provided with some countermeasure against flaws on discs, dust that adheres thereto or the like, as well as some countermeasure against vibrations or other mechanical external disturbances.
In a servo circuit concerning tracking controls and focus controls, in general, compromises involving opposite characteristics are known: an increase in the servo gain alleviates erroneous operations caused by vibrations but invites an excessive response against to disc flaws, dust, etc., which results in undesired movements of an optical pickup; and, in contrast, a decrease in the servo gain alleviates adverse influence from disc flaws but increases erroneous operations caused by vibrations.
In this connection, Japanese Patent Laid Open Publication No. Sho 60-74129, for example, discloses an apparatus which refers to a distortion in the waveform of an RF signal output from an optical pickup to decide whether the distortion has been caused by any disc flaw or dust, or by any vibration, thereby to decrease the servo gain in case of the former but increase the servo gain in case of the latter.
However, it is difficult to reliably decide from the RF signal waveform distortion the reason for the distortion because an RF signal distortion caused by disc flaws or dust may present an appearance as if it were caused by vibrations. This erroneous decision causes an increase of the servo gain, which is an adverse result opposite to the desired gain control (low gain). Therefore, it has been difficult to realize an apparatus less affected both by disc flaws or dust and by vibrations.